1. Field of the Invention
The present invention relates generally to a temperature changing apparatus, and in particular, relates to a temperature changing apparatus having an air mover, such as convection ovens, refrigerators, and freezers.
2. Description of the Related Art
A temperature changing apparatus, such as a convection oven, is used in the food industry to change the temperature of a food product as part of preparing the food for consumption. Convection ovens are provided as stand alone units or in combination with other food preparation mechanisms, such as steamers, in combination oven/steamers, such as those commercially available from Alto-Shaam®, Inc, located in Menomomee Falls, Wis. These combination devices include, in particular, Combitherm® Combination Oven/Steamers available from Alto-Shaam®, Inc., which utilize steam, heated air or a combination of both for steaming, baking, roasting, thawing, reheating, and various other cooking functions. These convection ovens are commercially available as gas and electric models.
Convection ovens decrease cooking time of food products by blowing heated air over a food product. The convection current caused by the moving heated air continuously strips away a cold boundary layer surrounding the food product and cooks the food product faster compared to a convention oven in which the air is static.
Known convection ovens, and other temperature changing apparatus, incorporate a centrifugal fan, or blower wheel, that continuously moves the air surrounding the food product in the oven to create the heated convection current. The centrifugal fan creates a flow pattern around the food product in the oven forming high and low pressure areas that are substantially static (i.e. the pressure areas do not move within the oven). As a result, different shaped food products and placement of the food product in the oven may affect the cooking time and result in uneven heating, an even uneven browning, of the food product. In the case of a refrigeration unit, the static pressure areas can affect the cooling and/or freezing time resulting in uneven cooling of the food product.
In order to overcome this problem, a static air baffle enclosing the centrifugal fan is often used. The static air baffle is often configured to produce a substantially laminar flow through the oven for cooking. Unfortunately, the baffle merely shapes the airflow to minimize the undesirable pressure areas for heating specifically shaped and placed food products. In particular, the baffle can be configured to direct laminar airflow equally along every shelf position in the oven for a low profile food product, such as a pan of cookies. Unfortunately, this same airflow would be unsatisfactory for another product, such as a sub roll or chicken breast, in the same oven.
In another attempt to disrupt the pressure areas in conventional convection ovens, some manufacturers intermittently stop and reverse the centrifugal fan. Stopping and reversing the centrifugal fan every few minutes reverse the air flow in the oven every few minutes and temporarily relocates the pressures areas. The pressure areas are only temporarily relocated because once the fan reaches its design speed, the location of the pressure areas is substantially the same regardless of the rotation direction of the fan. Unfortunately, stopping and reversing the centrifugal fan can create excessive noise and cause premature failure of the fan. Accordingly, this solution is less than desirable.
Therefore, a need exists for a convection oven that minimizes static pressure areas to efficiently and effectively heat a food product regardless of the food product shape or location in the oven.